The line circuit breaker has a housing. A switching device with a switch that can switch on and off and a combined overcurrent short-circuit current tripping device are arranged in the housing. Such a combined overcurrent short-circuit current tripping device was developed in order to use the smallest possible components. It includes on the one hand an armature and on the other hand a magnet yoke, to which a bimetallic element is fastened, through which current flows when the switch is switched on. A field line outlet plate is also arranged on the magnet yoke, on which field line outlet plate magnetic field lines outgoing from the magnet yoke during current flow and guided by the magnet yoke appear. The bimetallic element is arranged on a first side of the armature. In the uninterrupted system, it deforms in the case of an overcurrent and presses on the armature. The field line outlet plate is arranged on an opposite second side of the armature. In the case of a short-circuit current, it magnetically attracts the armature. The armature is thus rotated out of a rotational position at rest in the same predetermined direction both with an overcurrent and also with a short circuit current. With one rotation, it can cause the switch to switch off, for instance by way of a ratchet mechanism.
Cost-effective housing materials, like duroplasts (inter alia aminoplasts) for instance, are subject to a housing shrinkage during the course of the service life of the device. This is problematical because many components are to be mounted on the housing. The housing shrinkage results in the gaps between the components changing in respect of one another. This may have a negative influence on the thermal tripping (overcurrent tripping) and the magnetic tripping (short circuit current tripping).
The problem was previously regularly solved in that the whole switching mechanism was mounted in metal, so that the housing shrinkage could have no influence on the tripping. These constructions are very expensive.
Alternatively, low-shrink or shrink-free housing masses, for instance melamine masses, were used. This solution is also more expensive than the use of shrinkage-prone duoplast masses.